An Earthquake is the sudden often times violent shaking of the ground caused by high energy waves (seismic waves)
passing underneath your feet. These high energy waves are called seismic waves and they are the result of a massive slab of rock breaking as a result of stress built up in the Earth. When the rocks break, two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault. The location below the earth’s surface where the earthquake starts is called the focus or sometimes also called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter. Click on the animation to the right to understand what happens wheen an earthquake goes off; where is the epicenter? Where is the focus? Where was the fault and how did the siesmic waves move? When earth scientists and geologists locate earthquakes, they look for the epicenter. If you are standing at an earthquakes epicenter, then somewhere beneath your feet is the focus. The focus is the location in the earth where the actual energy from the earthquake is released in the form of seismic waves; moving outward in all directions, like a pebble between dropped in a pond, sending ripples outward in all directions.
Where do Earthquakes Occur?
The world's earthquakes are not randomly distributed over the Earth's surface. They tend occur in certain regions or areas around plate boundaries. Why is this? As tectonic plates move, their edges experience stress. If part of a plate cannot move freely, energy from the stress on the rocks builds up.
Click the buttons on the diagram to the right to reveal an overlay of plate boundaries and earthquake locations on the world map. Examine how the two patterns are related. What do you notice about the patterns of earthquake locations and it's relation to the of plate boundaries? Remember stress on rock is greatest at plate boundaries. At some point, the stress becomes so great that it breaks rock along a fault, causing an earthquake. Faults occur at plate boundaries where stress on rock is greatest.Their are three types of faults: Normal, Reverse, and Strike-Slip. Normal Faults are the cracks where one block of rock is pulled downward and away from another block of rock. The force responsible for creating these faults is tension, which pulls the blocks apart. Reverse Faults (also known as thrust faults) are cracks where one block of rock is pushed upward and towards the other block of rock. The force responsible for creating reverse faults is compression, which pushes the blocks together. Strike -Slip Faults are cracks where one block of rock is slides along the other block of rock. The force responsible for creating strike slip faults is shearing, which pushes the blocks parallel to the surface in opposite directions.
Measuring Earthquakes
Whenever a major earthquake is in the news, you'll probably hear about its Richter Scale rating. You might also hear about its Mercalli Scale rating, though this isn't discussed as often. These two ratings describe the power of the earthquake from two different perspectives. The most common standard of measurement for an earthquake is the Richter scale, developed in 1935 by Charles F. Richter of the California Institute of Technology. The Richter scale is used to rate the magnitude of an earthquake -- the amount of energy it released. This is calculated using information gathered by a seismometer or seimograph. When the ground shakes during an earthquake, a needle records the the degree of magnitude of shaking. In other words, the more the ground shakes, the more the needle sways back and forth recording the size or magnitude of an earthquake.
The Richter scale is exponential in it's scale. The amount of energy released increases 31.7 times between whole number values. So a Richter magnitude 6 earthquake releases 31.7 times more energy than a magnitude 5 earthquake. A Richter magnitude 7 releases roughly 1000 times more energy (31.7 x 31.7 = 1004) than a Richter magnitude 5 earthquake.
Many people don't realize this but the Earth produces millions of earthquakes a year; most of these quakes however, are microquakes (Richter magnitude 0.1-1.9) or minorquakes (Richter magnitude 2.0 - 3.9) and are usually not felt. These quakes, though small, are recorded by sensitive seismographs or seismometers. As the earthquakes become stronger, they also become more infrequent. Most people begin to feel and notice earthquakes at around a Richter magnitude of 4.0. A Richter magnitude 5.0 - 5.9 can be destructive if the quake strike a city with poorly built buildings. As you might have guessed earthquakes with a Richter magnitude from 6.0 - 7.9 can cause some serious damage and generate tsunamis. Earthquakes larger than a 7.9 can be devastating and cause serious loss of life; luckily these earthquakes only occur on average 1 per year.
The Richter magnitude scale only gives you a rough idea of the actual impact of an earthquake, though. As we've seen, an earthquake's destructive power varies depending on the composition of the ground in an area and the design and placement of man-made structures. The extent of damage is rated on the Mercalli scale. Mercalli ratings, which are given as Roman numerals, are based on largely subjective interpretations. A low intensity earthquake, one in which only some people feel the vibration and there is no significant property damage, is rated as a II. The highest rating, a XII, is applied to earthquakes in which structures are destroyed, the is cracked and other natural disasters, such as landslides or tsunamis, are initiated.
Richter scale ratings are determined soon after an earthquake, once scientists can compare the data from different seismograph stations. Mercalli ratings, on the other hand, can't be determined until investigators have had time to talk to many eyewitnesses to find out what occurred during the earthquake. Once they have a good idea of the range of damage, they use the Mercalli criteria to decide on an appropriate rating.
Mercalli Activity
Recent Earthquake Activity in California
Generously provided by Southern California Earthquake Data Center
How many Earthquakes are micro quakes (magnitude 0.1 - 1.9)?
How many Earthquakes are minor quakes (magnitude 2 - 3.9)?
How many Earthquakes are light quakes (magnitude 4.0 - 4.9)?
How many Earthquakes are moderate quakes (magnitude 2 - 3.9)?
How many earthquakes happened in the last hour?
How many earthquakes happened today?
Every earthquake releases seismic waves from it's focus or hypocenter. These seismic waves travel outward in all directions where they are recorded at seismic stations. There are three types of seismic waves: primary waves or P-waves for short, secondary waves or S-waves for short short, and surface waves. P waves, also called compressional waves or primary waves, move through material by squeezing and stretching the material in the same direction as the wave is moving. S waves, also called shear waves or secondary waves, move material perpendicular or up and down. Try to click on the animations below at the same time to examine the relative speeds of the waves. What wave traveled at a higher velocity or speed? What wave traveled at a lower velocity or speed? Hopefully you came to the conclusion that P-waves are faster than S-waves. The last type of seismic waves are called surface waves and these waves travel at the surface of the earth. These are the slowest of the three waves, and move rock is a circular motion. Because of their ability to travel at the surface of the Earth and severely shake the ground; these waves are responsible for creating much of the damage during a major earthquake.
Seismic Wave Simulator:
Can you create the 3 types of Seismic Waves?
Locating Earthquakes
To find the location of an earthquake's epicenter, scientists use the arrival times of different speeds of seismic waves.If you recall, earthquakes are measured with a seismometer or seismograph. View the animation, which waves are recorded first? Which waves are recorded second? Which waves are recorded last? Hopefully you noticed that the P-waves are recorded first, and S-waves are recorded second, and the deadly Surface waves, the slowest of the 3 seismic waves are recorded last. The time delay between the P and S wave is called the S-P time lag delay conveniently, and the farther you are from the earthquake epicenter, the greater the time delay. It's sort of like two cars traveling at different speeds, as these two cars leave their from there starting point, the faster car moves out ahead and gets farther away from the slower car as time goes by. Well, as P and S waves are released from an earthquake's epicenter, the P-wave moves out farther ahead of the S-wave as time goes by; increasing the time lag delay between the two waves as time goes by. Click play on the animation to the left; which sesimic station, A or B recorded a smaller S-P time lag delay? Which seismic station, A or B, recorded a greater time lag delay or lag time? Using the S-P time delay scientists are able to locate an earthquake's epicenter using 3 seismic locations from 3 seismometers. This process is called triangulation, which uses the S-P time delay or lag from 3 seismic locations to determine the location of an earthquake's epicenter. A graph is used to convert time into distance. Think about it, if you are driving 60mph, how far did you drive in one hour? 60 miles!!!! You just converted time into distance; which was scientist do when converting the S-P time lag delay into distance. Once the distance to each earthquake is known, scientists then plot this distance on a map using the data from three seismic stations. This distance is represented by drawing circles on a map. Where all three circles intersect, BINGO earthquake epicenter!!!!! View the animation below to better understand the process of triangulation. Feel free to right click on the animation and select play to view it again.
Triangulation Animation
Earthquake Analysis Activity:
Can you locate an earthquake?
Article: Comparing Two Earthquakes
Do earthquakes kill people or do buildings? In this article we will two earthquakes the Loma prieta earthquake that occured in California (south bay area) in 1989 and the Haiti earthquake that occurred in 2010. We will look at how these Earthquakes are similar, but we will also examine how these earthquakes are different in their casualties and building structures.
Loma Prieta Earthquake of 1989
The magnitude 7.1 earthquake occurred on a section of the San Andreas Strike Slip fault system between the Pacific and North American Plates. The earthquake epicenter was located in the Santa Cruz Mountains in the South San Francisco Bay Area of California on October 17, 1989 at 5:04 pm Pacific Daylight Time. The exact epicenter location was 16 km (~10 miles) northeast of Santa Cruz and about 30 km (~19 miles) south of San Jose. The quake lasted for 10 to 15 seconds with an average surface-wave magnitude of 7.1, a moment magnitude of 6.9, and a Richter magnitude of 7.0. Ground shaking was sufficient enough to cause structural damage at distances of 100 km (~62 miles). (EERI 1989). The earthquake struck the bay area just before the third game of the World Series at Candlestick Park. It knocked out power to San Francisco, and the city was dark for the first time since the 1906 earthquake and fire, however, power was restored by October 20. At least 27 fires broke out across the city, including a major blaze in the Marina District where apartment buildings sank into the bay mud. Approximately 63 deaths were reported, 400 people were severely injured, and roughly 4,000 total injuries were logged. In the aftermath of the earthquake, 3,000 people were left homeless with around 12,000 homes and 2,600 businesses damaged or destroyed. The Loma Prieta Earthquake caused an estimated $6 billion in damage. (Stoffer 2005). On October 17, 1989, the magnitude 7.1 Loma Prieta earthquake struck the Santa Cruz Mountains in central California. Sixty miles away, in downtown San Francisco, the occupants of the Transamerica Pyramid were unnerved as the 49-story office building shook for more than a minute. U.S. Geological Survey (USGS) instruments, installed years earlier, showed that the top floor swayed more than 1 foot from side to side. However, no one was seriously injured, and the Transamerica Pyramid was not damaged. This famous San Francisco landmark had been designed and retrofitted to withstand even greater earthquake stresses, and that design worked as planned during the earthquake
Building Performance
When you consider the magnitude of the earthquake (7.1) and the death toll (63) aswell as the damage cost (estimated six billion dollars) California was for the most part prepared for this earthquake (Stoffer, 2005). The damage that did occur exposed poor building standards and poor location choice. The Marina District in San Francisco was built on fill made of sand, dirt and rubble, which underwent severe liquefaction and many buildings collapsed (Virtual Museum of the City of San Francisco, 2009). The Cypress Viaduct was built using non-ductile reinforced concrete and was also built on marshland which underwent liquefaction during the shaking.
The Loma Prieta earthquake also revealed a number of success stories in disaster mitigation. The main success was Candlestick Park which had recently undergone a seismic strengthening project and stood strong during the earthquake, sparing thousands of lives (Housner, 1990).
As a result of the major structural failures, San Francisco has been taking steps for mitigation, rebuilding, retrofitting old buildings, and strengthening structures in light of stricter building codes. The Loma Prieta earthquake revealed that buildings built before 1971 were easily collapsed (Nigg, et al, 1998). The California Earthquake Authority (CEA) plans to institute a state-wide residential seismic retrofit program. This program will offer homeowners the opportunity to take action to make their houses more seismically stable with the aid of a government rebate. Specialized training was given to contractors, engineers, and inspectors specifically towards seismic engineering (Parrish, et al., 2009). Base isolation, which isolates the building’s attachment to the ground from the superstructure above the ground, was installed in San Francisco International Airport and San Francisco’s city hall, the first and second largest base isolated structures in the world respectively (SFGov, 2009).
The most vital mitigation that is taking place is being undertaken by the utility companies of San Francisco. Many companies are taking steps to safeguard their water, electricity, transportation, and communication systems, many of which were lost during Loma Prieta. California’s highway company, Caltrans, is strengthening bay bridges, freeway sections, and overpasses, PG&E is working to be sure that power and gas systems will not fail during a quake, and there has been an upgrade to the emergency water system (Bakun, 1995). Clearly, many mitigation and retrofitting steps have been taken as a result of the Loma Prieta earthquake.
Haiti Earthquake of 2010
The 2010 Haiti earthquake was a catastrophic magnitude 7.0 earthquake that occurred on a strike-slip fault line between the Caribbean and North American plates. The epicenter was located approximately 25 km (16 miles) west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time (21:53 UTC) on Tuesday, 12 January 2010. By 24 January, at least 52 aftershocks measuring 4.5 or greater had been recorded.[9] An estimated three million people were affected by the quake. Death toll estimates ranges from 159,000 to Haitian figures of 220,000. Haiti's magnitude 7.0 earthquake struck a country whose buildings were barely built to engineering standards and were hopelessly fragile in the grip of such a strong quake. That's the assessment of Pierre Fouche, an earthquake engineer from Haiti — in fact, the country's only earthquake engineer, to his knowledge. Fouche says when he was studying engineering in Haiti his professors told him that at least one building there would survive an earthquake — the presidential residence known as the National Palace. The palace now lies in ruins.
Building Performance
Fouche is now getting his doctorate in earthquake engineering at the University of Buffalo. He says his family has survived Tuesday's quake, but he's saddened by the fact that so many who didn't were killed because buildings in Haiti are so poorly constructed. "Many people are doing whatever they want; they can build whatever they want," Fouche says. "One of the biggest problems too is that in the country we do not even have a national building code, which is very sad." Fouche says people with money can build reinforced concrete buildings with steel rods to strengthen walls and floors. But he says even these may not meet engineering standards to support a load vertically, and they definitely cannot handle the side-to-side forces of an earthquake. "The earthquake, it's much more of a type of lateral loading, [and] for lateral loading you need special construction, but in many cases they are not designed, not even for current daily loading." But many people in Haiti live and work in unreinforced buildings — brick, block or concrete. He says some of these buildings use stacked bricks instead of solid vertical columns to support ceilings. Earthquakes put enormous stress on rigid buildings. Andre Filiatrault, who directs the earthquake engineering center at the University of Buffalo, explains what happens to a masonry or concrete wall that's perpendicular to the motion of the quake: "The wall just kind of explodes. Imagine that I hit a wall with my fist; I'm going to create a hole there, and imagine [that] the shaking in that direction will create even a bigger hole and the wall collapses and the slab falls down." The slab being the wall or ceiling.
Filiatraut says televised images of Port-au-Prince suggest this kind of collapse was widespread. "The video showed complete dust over the entire city. Apparently that dust lasted quite a long time, 10, 15 minutes or so, and that seems to indicate these types of buildings, concrete buildings, pancaking, creating a lot of dust." Several big aftershocks followed the earthquake. Fouche says that makes the surviving buildings very dangerous. "Once you have the aftershock," he says, "it's like you are shaking a building that is already damaged, so this is quite likely to bring those buildings down." So, why did so many people die in the Haiti earthquake?
The earthquake occurred at shallow depth - this means that the seismic waves have to travel a smaller distance through the earth to reach the surface so maintain more of their energy.
Haiti is the poorest country in the Western Hemisphere
The buildings in Port-Au-Prince and other areas of Haiti were in very poor condition in general and were not designed or constructed to be earthquake resistant.
3 Million people live in Port Au Prince with the majority living in slum conditions after rapid urbanization.
Haiti only has one airport with one runway. The control tower was badly damaged in the earthquake. The port is also unusable due to damage.
Initially, aid had been piling up at the airport due to a lack of trucks and people to distribute it. Water and food have taken days to arrive and there is not enough to go around.
Rescue teams from around the world took up to 48 hours to arrive in Haiti due to the problems at the airport. Local people have had to use their bare hands to try and dig people out of the rubble.
There has been a severe shortage of doctors and many people have died of injuries such as broken limbs, disease, and dysntery.
Data Summary
Earthquake Comparisons
Magnitude
Deaths
Damages
Country
1989 Loma Prieta
7.1
62
$6 Billion
Developed wealthy
2010 Haiti
7.0
220,000
$14 Billion
Developing poor
Day 4
Project Earthquake Discussion Forum
You are just about done with your project. But first you need to visit the online discussion forum below and thoroughly answer one of the questions below in detail citing evidence. Remember, these questions should not be difficult because you have already done research. When you are finished, you are required to read and grade your lab groups responses. Use the rubric below to guide you through the grading process:
What or Earthquakes and where do they occur?
What are some of the different ways we measure and locate earthquake?
What is an Earthquake?
An Earthquake is the sudden often times violent shaking of the ground caused by high energy waves (seismic waves)passing underneath your feet. These high energy waves are called seismic waves and they are the result of a massive slab of rock breaking as a result of stress
Where do Earthquakes Occur?
The world's earthquakes are not randomly distributed over the Earth's surface. They tend occur in certain regions or areas around plate boundaries. Why is this? As tectonic plates move, their edges experience stress. If part of a plate cannot move freely, energy from the stress on the rocks builds up.Click the buttons on the diagram to the right to reveal an overlay of plate boundaries and earthquake locations on the world map. Examine how the two patterns are related. What do you notice about the patterns of earthquake locations and it's relation to the of plate boundaries? Remember stress on rock is greatest at plate boundaries. At some point, the stress becomes so great that it breaks rock along a fault, causing an earthquake. Faults occur at plate boundaries where stress on rock is greatest.Their are three types of faults: Normal, Reverse, and Strike-Slip. Normal Faults are the cracks where one block of rock is pulled downward and away from another block of rock. The force responsible for creating these faults is tension, which pulls the blocks apart. Reverse Faults (also known as thrust faults) are cracks where one block of rock is pushed upward and towards the other block of rock. The force responsible for creating reverse faults is compression, which pushes the blocks together. Strike -Slip Faults are cracks where one block of rock is slides along the other block of rock. The force responsible for creating strike slip faults is shearing, which pushes the blocks parallel to the surface in opposite directions.
Measuring Earthquakes
Whenever a major earthquake is in the news, you'll probably hear about its Richter Scale rating. You might also hear about its Mercalli Scale rating, though this isn't discussed as often. These two ratings describe the power of the earthquake from two different perspectives. The most common standard of measurement for anearthquake is the Richter scale, developed in 1935 by Charles F. Richter of the California Institute of Technology. The Richter scale is used to rate the magnitude of an earthquake -- the amount of energy it released. This is calculated using information gathered by a seismometer or seimograph. When the ground shakes during an earthquake, a needle records the the degree of magnitude of shaking. In other words, the more the ground shakes, the more the needle sways back and forth recording the size or magnitude of an earthquake.
The Richter scale is exponential in it's scale. The amount of energy released increases 31.7 times between whole number values. So a Richter magnitude 6 earthquake releases 31.7 times more energy than a magnitude 5 earthquake. A Richter magnitude 7 releases roughly 1000 times more energy (31.7 x 31.7 = 1004) than a Richter magnitude 5 earthquake.
Many people don't realize this but the Earth produces millions of earthquakes a year; most of these quakes however, are microquakes (Richter magnitude 0.1-1.9) or minorquakes (Richter magnitude 2.0 - 3.9) and are usually not felt. These quakes, though small, are recorded by sensitive seismographs or seismometers. As the earthquakes become stronger, they also become more infrequent. Most people begin to feel and notice earthquakes at around a Richter magnitude of 4.0. A Richter magnitude 5.0 - 5.9 can be destructive if the quake strike a city with poorly built buildings. As you might have guessed earthquakes with a Richter magnitude from 6.0 - 7.9 can cause some serious damage and generate tsunamis. Earthquakes larger than a 7.9 can be devastating and cause serious loss of life; luckily these earthquakes only occur on average 1 per year.
The Richter magnitude scale only gives you a rough idea of the actual impact of an earthquake, though. As we've seen, an earthquake's destructive power varies depending on the composition of the ground in an area and the design and placement of man-made structures. The extent of damage is rated on the Mercalli scale. Mercalli ratings, which are given as Roman numerals, are based on largely subjective interpretations. A low intensity earthquake, one in which only some people feel the vibration and there is no significant property damage, is rated as a II. The highest rating, a XII, is applied to earthquakes in which structures are destroyed, the is cracked and other natural disasters, such as landslides or tsunamis, are initiated.
Richter scale ratings are determined soon after an earthquake, once scientists can compare the data from different seismograph stations. Mercalli ratings, on the other hand, can't be determined until investigators have had time to talk to many eyewitnesses to find out what occurred during the earthquake. Once they have a good idea of the range of damage, they use the Mercalli criteria to decide on an appropriate rating.
Mercalli Activity
Recent Earthquake Activity in CaliforniaGenerously provided by Southern California Earthquake Data Center
How many Earthquakes are micro quakes (magnitude 0.1 - 1.9)?How many Earthquakes are minor quakes (magnitude 2 - 3.9)?
How many Earthquakes are light quakes (magnitude 4.0 - 4.9)?
How many Earthquakes are moderate quakes (magnitude 2 - 3.9)?
How many earthquakes happened in the last hour?
How many earthquakes happened today?
For more Information please click go to: http://www.data.scec.org/
Day 2
Seismic Waves
Every earthquake releases seismic waves from it's focus or hypocenter. These seismic waves travel outward in all directions where they are recorded at seismic stations. There are three types of seismic waves: primary waves or P-waves for short, secondary waves or S-waves for short short, and surface waves. P waves, also called compressional waves or primary waves, move through material by squeezing and stretching the material in the same direction as the wave is moving. S waves, also called shear waves or secondary waves, move material perpendicular or up and down. Try to click on the animations below at the same time to examine the relative speeds of the waves. What wave traveled at a higher velocity or speed? What wave traveled at a lower velocity or speed? Hopefully you came to the conclusion that P-waves are faster than S-waves. The last type of seismic waves are called surface waves and these waves travel at the surface of the earth. These are the slowest of the three waves, and move rock is a circular motion. Because of their ability to travel at the surface of the Earth and severely shake the ground; these waves are responsible for creating much of the damage during a major earthquake.Seismic Wave Simulator:
Can you create the 3 types of Seismic Waves?
Locating Earthquakes
To find the location of an earthquake's epicenter, scientists use the arrival times of different speeds of seismic waves.If you recall, earthquakes are measured with a seismometer or seismograph. View the animation, which waves are recorded first? Which waves are recorded second? Which waves are recorded last? Hopefully you noticed that the P-waves are recorded first, and S-waves are recorded second, and the deadly Surface waves, the slowest of the 3 seismic waves are recorded last. The time delay between the P and S wave is called the S-P time lag delay conveniently, and the farther you are from the earthquake epicenter, the greater the time delay. It's sort of like two cars traveling at different speeds, as these two cars leave their from there starting point, the faster car moves out ahead and gets farther away from the slower car as time goes by. Well, as P and S waves are released from an earthquake's epicenter, the P-wave moves out farther ahead of the S-wave as time goes by; increasing the time lag delay between the two waves as time goes by. Click play on the animation to the left; which sesimic station, A or B recorded a smaller S-P time lag delay? Which seismic station, A or B, recorded a greater time lag delay or lag time? Using the S-P time delay scientists are able to locate an earthquake's epicenter using 3 seismic locations from 3 seismometers. This process is called triangulation, which uses the S-P time delay or lag from 3 seismic locations to determine the location of an earthquake's epicenter. A graph is used to convert time into distance. Think about it, if you are driving 60mph, how far did you drive in one hour? 60 miles!!!! You just converted time into distance; which was scientist do when converting the S-P time lag delay into distance. Once the distance to each earthquake is known, scientists then plot this distance on a map using the data from three seismic stations. This distance is represented by drawing circles on a map. Where all three circles intersect, BINGO earthquake epicenter!!!!! View the animation below to better understand the process of triangulation. Feel free to right click on the animation and select play to view it again.Triangulation Animation
Earthquake Analysis Activity:
Can you locate an earthquake?
Article: Comparing Two Earthquakes
Do earthquakes kill people or do buildings? In this article we will two earthquakes the Loma prieta earthquake that occured in California (south bay area) in 1989 and the Haiti earthquake that occurred in 2010. We will look at how these Earthquakes are similar, but we will also examine how these earthquakes are different in their casualties and building structures.Loma Prieta Earthquake of 1989
The magnitude 7.1 earthquake occurred on a section of the San Andreas Strike Slip fault system between the Pacific and North American Plates. The earthquake epicenter was located in the Santa Cruz Mountains in the South San Francisco Bay Area of California on October 17, 1989 at 5:04 pm Pacific Daylight Time. The exact epicenter location was 16
km (~10 miles) northeast of Santa Cruz and about 30 km (~19 miles) south of San Jose. The quake lasted for 10 to 15 seconds with an average surface-wave magnitude of 7.1, a moment magnitude of 6.9, and a Richter magnitude of 7.0. Ground shaking was sufficient enough to cause structural damage at distances of 100 km (~62 miles). (EERI 1989). The earthquake struck the bay area just before the third game of the World Series at Candlestick Park. It knocked out power to San Francisco, and the city was dark for the first time since the 1906 earthquake and fire, however, power was restored by October 20. At least 27 fires broke out across the city, including a major blaze in the Marina District where apartment buildings sank into the bay mud. Approximately 63 deaths were reported, 400 people were severely injured, and roughly 4,000 total injuries were logged. In the aftermath of the earthquake, 3,000 people were left homeless with around 12,000 homes and 2,600 businesses damaged or destroyed. The Loma Prieta Earthquake caused an estimated $6 billion in damage. (Stoffer 2005). On October 17, 1989, the magnitude 7.1 Loma Prieta earthquake struck the Santa Cruz Mountains in central California. Sixty miles away, in downtown San Francisco, the occupants of the Transamerica Pyramid were unnerved as the 49-story office building shook for more than a minute. U.S. Geological Survey (USGS) instruments, installed years earlier, showed that the top floor swayed more than 1 foot from side to side. However, no one was seriously injured, and the Transamerica Pyramid was not damaged. This famous San Francisco landmark had been designed and retrofitted to withstand even greater earthquake stresses, and that design worked as planned during the earthquake
Building Performance
When you consider the magnitude of the earthquake (7.1) and the death toll (63) aswell as the damage cost (estimated six billion dollars) California was for the most part prepared for this earthquake (Stoffer, 2005). The damage that did occur exposed poor building standards and poor location choice. The Marina District in San Francisco was built on fill made of sand, dirt and rubble, which underwent severe liquefaction and many buildings collapsed (Virtual Museum of the City of San Francisco, 2009). The Cypress Viaduct was built using non-ductile reinforced concrete and was also built on marshland which underwent liquefaction during the shaking.
The Loma Prieta earthquake also revealed a number of success stories in disaster mitigation. The main success was Candlestick Park which had recently undergone a seismic strengthening project and stood strong during the earthquake, sparing thousands of lives (Housner, 1990).
As a result of the major structural failures, San Francisco has been taking steps for mitigation, rebuilding, retrofitting old buildings, and strengthening structures in light of stricter building codes. The Loma Prieta earthquake revealed that buildings built before 1971 were easily collapsed (Nigg, et al, 1998). The California Earthquake Authority (CEA) plans to institute a state-wide residential seismic retrofit program. This program will offer homeowners the opportunity to take action to make their houses more seismically stable with the aid of a government rebate. Specialized training was given to contractors, engineers, and inspectors specifically towards seismic engineering (Parrish, et al., 2009). Base isolation, which isolates the building’s attachment to the ground from the superstructure above the ground, was installed in San Francisco International Airport and San Francisco’s city hall, the first and second largest base isolated structures in the world respectively (SFGov, 2009).
The most vital mitigation that is taking place is being undertaken by the utility companies of San Francisco. Many companies are taking steps to safeguard their water, electricity, transportation, and communication systems, many of which were lost during Loma Prieta. California’s highway company, Caltrans, is strengthening bay bridges, freeway sections, and overpasses, PG&E is working to be sure that power and gas systems will not fail during a quake, and there has been an upgrade to the emergency water system (Bakun, 1995). Clearly, many mitigation and retrofitting steps have been taken as a result of the Loma Prieta earthquake.
Haiti Earthquake of 2010
The 2010 Haiti earthquake was a catastrophic magnitude 7.0 earthquake that occurred on a strike-slip fault line between the Caribbean and North American plates. The epicenter was located approximately 25 km (16 miles) west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time (21:53 UTC) on Tuesday, 12 January 2010. By 24 January, at least 52 aftershocks measuring 4.5 or greater had been recorded.[9] An estimated three million people were affected by the quake. Death toll estimates ranges from 159,000 to Haitian
Building Performance
Fouche is now getting his doctorate in earthquake engineering at the University of Buffalo. He says his family has survived Tuesday's quake, but he's saddened by the fact that so many who didn't were killed because buildings in Haiti are so poorly constructed. "Many people are doing whatever they want; they can build whatever they want," Fouche says. "One of the biggest problems too is that in the country we do not even have a national building code, which is very sad." Fouche says people with money can build reinforced concrete buildings with steel rods to strengthen walls and floors. But he says even these may not meet engineering standards to support a load vertically, and they definitely cannot handle the side-to-side forces of an earthquake. "The earthquake, it's much more of a type of lateral loading, [and] for lateral loading you need special construction, but in many cases they are not designed, not even for current daily loading." But many people in Haiti live and work in unreinforced buildings — brick, block or concrete. He says some of these buildings use stacked bricks instead of solid vertical columns to support ceilings. Earthquakes put enormous stress on rigid buildings. Andre Filiatrault, who directs the earthquake engineering center at the University of Buffalo, explains what happens to a masonry or concrete wall that's perpendicular to the motion of the quake: "The wall just kind of explodes. Imagine that I hit a wall with my fist; I'm going to create a hole there, and imagine [that] the shaking in that direction will create even a bigger hole and the wall collapses and the slab falls down." The slab being the wall or ceiling.
Filiatraut says televised images of Port-au-Prince suggest this kind of collapse was widespread. "The video showed complete dust over the entire city. Apparently that dust lasted quite a long time, 10, 15 minutes or so, and that seems to indicate these types of buildings, concrete buildings, pancaking, creating a lot of dust." Several big aftershocks followed the earthquake. Fouche says that makes the surviving buildings very dangerous. "Once you have the aftershock," he says, "it's like you are shaking a building that is already damaged, so this is quite likely to bring those buildings down." So, why did so many people die in the Haiti earthquake?
Data Summary
Day 4
Project Earthquake Discussion Forum
You are just about done with your project. But first you need to visit the online discussion forum below and thoroughly answer one of the questions below in detail citing evidence. Remember, these questions should not be difficult because you have already done research. When you are finished, you are required to read and grade your lab groups responses. Use the rubric below to guide you through the grading process:Project Earthquake Discusion Forum